Disposable diaper and process for making the same

ABSTRACT

A disposable diaper has a covering member adapted to cover a wearer&#39;s crotch and waist regions. The covering member includes an elastically stretchable first layer and an inelastically stretchable second layer formed with a plurality of continuous fibers. The continuous fibers are fixed to the first layer in at least two bonding zones. The covering member presents a particularly large value of L/D, a ratio of a length L of each continuous fiber and a distance D in straight line between each pair of the adjacent bonding zones.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a disposable diaper and a process for making the same.

[0002] Japanese Patent Application Publication No. 1991-162854A describes pants-type or brief-type undergarment comprising an elastically stretchable topsheet, an elastically stretchable backsheet, elastic members extending along transversely opposite side edge portions of a crotch region to be associated with leg-openings and elastic members extending longitudinally opposite end portions of front and rear waist regions to be associated with a waist-opening. A water-absorbent core member may be disposed between the topsheet and the backsheet to use this undergarment as a disposable diaper. With such diaper, according to the description in the Publication, elastic stretchability of the topsheet and the backsheet serves to offer a good fitness and the sealing effect of the elastic members associated with the leg-openings serves to prevent leaking sideways of excretion from occurring along the leg-openings as the diaper is put on the wearer's body.

[0003] The disposable diaper of prior art enables the topsheet and the backsheet to be stretched so as to offer good fitness around the wearer's waist as the diaper is put on the wearer's body. However, stretching of these topsheet and the backsheet affects the vicinity of the elastic members associated with the leg-openings and tends to partially disengage these elastic members from the wearer's legs, in other words, to deteriorate the sealing effect of these elastic members. In consequence, there is an anxiety that sideway leak of excretion might occur along the elastic members associated with the leg-openings.

SUMMARY OF THE INVENTION

[0004] It is an object of this invention to improve the conventional a disposable diaper such as the above-mentioned diaper of prior art so that wearer's crotch and waist regions can be covered by an elastically stretchable covering member without deteriorating a desired effect of preventing excretion leakage from occurring around wearer's legs.

[0005] According to an aspect of this invention, there is provided a disposable diaper comprising an elastically stretchable covering member adapted to cover a wearer's crotch and waist regions and a liquid-absorbent core member sandwiched between a liquid-pervious sheet destined to come in contact with skin of the diaper wearer and the covering member.

[0006] The improvement according to this invention is in that the covering member consists of an elastically stretchable first layer and an inelastically stretchable second layer formed with a plurality of continuous fibers and the continuous fibers being fixed to the first layer in at least a pair of bonding zones spaced apart from each other so that L/D, i.e., a ratio of a length L of the continuous fiber extending between the pair of the bonding zones to a distance D in straight line between the pair of bonding zones is larger in a desired range of the covering member than in the remaining zone.

[0007] According to another aspect of this invention, by an improvement in the process for making a disposable diaper comprising an elastically stretchable covering member adapted to cover diaper wearer s crotch and waist regions and a liquid-absorbent core member sandwiched between a liquid-pervious sheet destined to come in contact with skin of the diaper wearer and the covering member.

[0008] The improvement according to this invention comprises steps of bonding an elastically stretchable first layer destined to form the covering member and a second layer formed with a plurality of inelastically stretchable continuous fibers together in a plurality of intermittently formed bonding zones and thereby to form a composite sheet, stretching only a portion of the composite sheet in one direction so that the first layer forming the portion may be elastically stretched together with the continuous fibers, and then leaving the composite sheet contract under a contractile force of the first layer to form the covering member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a plan view of disposable diaper as partially broken away;

[0010]FIG. 2 is a sectional view taken along a line II-II in FIG. 1;

[0011]FIG. 3 is a sectional view taken along a line III-III in FIG. 1;

[0012]FIG. 4 is a fragmentary perspective view of a backsheet;

[0013]FIG. 5 is a diagram illustrating a process for making the backsheet;

[0014]FIG. 6 is a view similar to FIG. 1 showing one preferred embodiment of this invention; and

[0015]FIG. 7 is a sectional view taken along a line VII-VII in FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Details of the disposable diaper and the process for making the same proposed by this invention will be more fully understood from the description given hereunder with reference to the accompanying drawings.

[0017] A disposable diaper 1 shown by FIG. 1 in a plan view as partially broken away comprises a liquid-pervious topsheet 2, a liquid-impervious backsheet 3 and a body fluid absorbent core member 4 disposed between the topsheet 2 and the backsheet 3 is formed with an inside sheet 3 a and an outside sheet 3 b. Regarding its configuration, the diaper 1 is composed, in its longitudinal direction, of a front waist region 6, a rear waist region 7 and a crotch region 8 extending between these two waist regions 6, 7. The topsheet 2 and the backsheet 3 are placed upon and bonded to each other over their portions extending outward beyond a peripheral edge of the core member 4 so as to form a front flap 11, a rear flap 12 and a pair of side flaps 13 adapted to cover a crotch and a waist of a diaper wearer. The rear flap 12 has an elastic member 16 extending transversely of the diaper 1 and bonded under tension to inner surface of at least one of the topsheet 2 and the backsheet 3 in order to be associated with a waist-opening. The side flaps 13 have elastic members 17 extending longitudinally of the diaper 1 and bonded under tension to the inner surface of at least one of the topsheet 2 and the backsheet 3 in order to be associated with respective leg-openings. In the rear waist region 7, a pair of tape fasteners 18 are attached to side edge portions of the side flaps 13, respectively.

[0018] The topsheet 2 is elastically stretchable and may be formed, for example, with a nonwoven fabric made of elastically stretchable filaments. The topsheet 2 is elastically stretchable at least transversely of the diaper 1 and, more preferably, in length as well as in width.

[0019] Of the backsheet 3, the inside sheet 3 a is liquid-impervious and formed with a sheet being elastically stretchable transversely of the diaper 1 and, more preferably, in length as well as in width. The outside sheet 3 b comprises a plurality of inelastically stretchable continuous fibers 20 (See FIG. 4) accumulated on one surface of the inside sheet 3 a to form a sheet and bonded to the one surface in a plurality of bonding zones 21 (See FIG. 4).

[0020]FIGS. 2 and 3 are sectional views taken along lines II-II and III-III in FIG. 1, respectively. In the diaper 1, the backsheet 3 is substantially flat and the core member 4 protrudes from the backsheet 3 toward the topsheet 2 (downward as viewed in FIGS. 2 and 3). The backsheet 3 is divided transversely or longitudinally, at least transversely of the diaper 1 into a range A extending in the middle zone and ranges B extending on both sides of the range A so that the range A may be more easily stretched than the ranges B. According to one preferred embodiment, the transversely middle zone A presents a stress of 0.25˜2 N as measured on a test piece having a width of 25 mm as this zone A is stretched by 20%. This value is less than 80%, more preferably less than 50% of a stress presented by each of the ranges B as it is stretched by 20%. The topsheet 2, on the other hand, should be stretchable transversely of the diaper 1 as easily as or more easily than the range A of the backsheet 3. The range A extends to the vicinity of transversely opposite side edges 4 a, 4 a of the core member 4 transversely of the diaper 1 and extends substantially over a full length of the backsheet 3 longitudinally of the diaper 1.

[0021] Only the range A of the backsheet 3 is deformed as indicated by chain lines and the core member 4 shifts its position so as to protrude outwardly of the diaper 1 as the diaper 1 constructed as has been described above is put on a wearer's body with the topsheet 2 placed against the wearer's skin under pressure P exerted on the core member 4 (See FIGS. 2 and 3). The pressure P is adequately dampened by stretching of the range A to avoid an anxiety that the pressure might be exerted on the elastic members 17 for the leg-openings via the ranges B. Thus it is not apprehended that the desired fitness of the elastic members 17 around the legs might be adversely affected by the pressure P. In this way, the elastic members 17 associated with the leg-openings cooperate with the ranges B being less stretchable than the range A to maintain the desired fitness of the diaper 1 around the wearer's legs. It is unnecessary for such diaper 1 to use the elastic members 17 associated with the leg-openings having a relatively high stretch stress taking account of the influence of the pressure P. With such diaper 1, there is no anxiety that the elastic members 17 having a relatively high stretch stress might be unacceptably pressed around the wearer's legs.

[0022]FIG. 4 is a fragmentary perspective view of the backsheet 3. The inside sheet 3 a has a basis weight of 10˜100 g/m² and is formed with elastic material such as styrene-based elastomer or urethane-based elastomer. The outside sheet 3 b has a basis weight of 8˜50 g/m² and is formed by sheet-like accumulation of inelastically stretchable continuous fibers 20 such as those of polypropylene, ethylene/propylene copolymer or ethylene/propylene/butene copolymer. These in- and outside sheets 3 a, 3 b are bonded together in bonding zones 21 formed intermittently transversely of the diaper 1, more preferably, transversely and longitudinally of the diaper 1. In these bonding zones 21, the in- and outside sheets 3 a, 3 b are bonded together by fusion or adhesion.

[0023] Each of the continuous fibers 20 has a length L and describes a curve between each pair of the adjacent bonding zones 21, 21 in which the continuous fibers 20 are fixed to the inside sheet 3 a. D designates a distance in a straight line connecting each pair of the adjacent bonding zones 21, 21 and a ratio L/D is equal to 1 or larger. The ratio L/D in the range A of the backsheet 3 is larger than the ratio L/D in the ranges B. In other words, the range A is more easily stretchable than the ranges B transversely as well as longitudinally, at least transversely of the diaper 1. On an early stage of transversely stretching the backsheet 3, the inside sheet 3 a is elastically stretched in the range A and the continuous fibers 20 are reoriented to be straightened between the respective pairs of the adjacent bonding zones 21, 21 in which these continuous fibers 20 are fixed to the inside sheet 3 a. So far as the continuous fibers 20 are merely reoriented and substantially not stretched, force required to stretch only the inside sheet 3 a is sufficient to stretch the range A. Once the early stage has been completed and the continuous fibers 20 have been straightened, a considerable force to stretch the inside sheet 3 a together with the outside sheet 3 b comprising the continuous fibers 20 is required to stretch the range A. In the ranges B of the backsheet 3, on the other hand, L/D, i.e., a ratio the length L of the continuous fibers 20 to the distance D in a straight line between the respective pairs of the adjacent bonding zones 21, 21 is substantially smaller than L/D in the range A and therefore a considerable force required to stretch the inside sheet 3 a together with the outside sheet 3 b is required to stretch the backsheet 3 transversely of the diaper 1 already on the early stage of stretching the backsheet 3.

[0024] As has been described above, the topsheet 2 is elastically stretchable while the backsheet 3 has the range A requiring no large force to stretch it and the ranges B requiring a considerable force to stretch them. Accordingly, the pressure P exerted on the core member 4 by the wearer's body via the topsheet 2 as the diaper 1 is put on the wearer's body is well absorbed by stretching of the range A, as indicated by the imaginary lines in FIGS. 2 and 3. In this manner, there is substantially no possibility that the pressure P might be exerted on the ranges B also and affect the elastic members 17 associated with the leg-openings.

[0025]FIG. 5 is a diagram illustrating a part of the process for making the backsheet 3. In step I, continuous fibers 220 destined to form the outside sheet 3 b are discharged from a plurality of extruding nozzles (not illustrated) and accumulated onto one surface of elastically stretchable web 203 a destined to form the inside sheet 3 a of the backsheet 3. Then, a plurality of bonding zones 221 are intermittently formed in which these stretchable web 203 a and continuous fibers 220 are welded together to form composite web 200 which is, in turn, fed from the left as viewed in this diagram.

[0026] In step II, transversely opposite side edge regions 231 indicated by oblique lines of the composite web 200 are clamped so that these side edge portions 231 might be stretched in the subsequent steps.

[0027] In step III, a transversely middle region 232 of the composite web 200 which is free from the clamping effect is transversely stretched by at least 50% or more, preferably by 80% or more, more preferably by 200% or more. In this step III, the stretchable web 203 a is elastically stretched and the continuous fibers 220 are inelastically stretched between the respective pairs of the adjacent bonding zones 221, 221, in other words, stretched under plastic deformation. Along the transversely opposite side edge regions 231, both the stretchable web 203 a and the continuous fibers 220 are not stretched.

[0028] In step IV, the composite web 200 having been stretched is contracted under a contractile force of the stretchable web 203 a and thereafter the composite web 200 is unclamped.

[0029] The contracted composite web 200 obtained in the manner as has been described may be cut into an appropriate length to obtain the backsheet 3 of FIG. 1 wherein the middle region 232 and the side edge regions 231 of the composite web 200 define the inside sheet 3 a and the outside sheet 3 b of the backsheet 3, respectively. The continuous fibers 220 and the bonding zones 221 correspond to the continuous fibers 20 and the bonding zones 21, respectively. In the backsheet 3 obtained through these steps, the continuous fibers 20 extending within the range A have been stretched at a higher ratio than the continuous fibers 20 extending in the zones B and consequently the formers are thinner than the latters. The ratio L/D between each pair of the adjacent bonding zones 21, 21 is larger in the range A than the ratio L/D in the ranges B. The outside sheet 3 b comprising the continuous fibers 20 is more bulky in the range A than in the ranges B since the continuous fibers 20 have been stretched at a higher ratio in the range A than in the ranges B. The backsheet 3 offers more flexible and soft touch in the range A than in the ranges B.

[0030]FIG. 6 is a view similar to FIG. 1 showing one preferred embodiment of this invention and FIG. 7 is a sectional view taken along a line VII-VII in FIG. 6. The diaper 1 illustrated herein has a covering member 40 adapted to cover crotch and waist regions of the wearer and an absorbent member 45 adapted to absorb body fluids. The absorbent member 45 comprises a core member 44 lying inside the covering member 40, a liquid-pervious sheet 42 covering the core member 44 and destined to come in contact with the wearer's skin and a liquid-impervious sheet 43 lying on the side opposed to the liquid-pervious sheet 42 with the core member 44 therebetween. Both the liquid-pervious sheet 42 and the liquid-impervious sheet 43 are elastically stretchable preferably in the transverse direction, more preferably not only in the transverse direction but also in the longitudinal direction of the diaper 1. Portions of these sheets 42, 43 extending outward beyond a peripheral edge of the core member 44 are placed upon and bonded to each other by means of hot melt adhesive (not shown). The covering member 40 is longitudinally composed of a front waist region 46, a rear waist region 47 and a crotch region 48 extending between the front waist region 46 and the rear waist region 47. The liquid-impervious sheet 43 longitudinally extending outward beyond the peripheral edge of the core member 44 is bonded to inner surface of the covering member 40 along respective end portions 51, 52 thereof in the front waist region 46 and the rear waist region 47, also by means of hot melt adhesive (not shown). While the portion of the liquid-impervious sheet 43 extending between the end portions 51, 52 has been described to be bonded to the covering member 40 by means of hot melt adhesive, it is also possible to leave this portion not bonded to the covering member 40.

[0031] The covering member 40 comprises an elastically stretchable liquid-impervious inside sheet 40 a and an outside sheet 40 b formed with inelastically stretchable continuous fibers 20. These two sheets 40 a, 40 b are bonded together in a plurality of bonding zones 61 formed intermittently in the transverse and longitudinal directions, at least in the transverse direction of the diaper 1. Transverse stretchability of such covering member 40 is substantially similar to that of the backsheet 3 shown in FIGS. 1˜3. Specifically to describe, the covering member 40 has the range A defined in the transversely middle zone thereof and the ranges B defined on both sides of the range A. In the range A, the continuous fibers 20 have been stretched at a relatively high ratio so that the covering member 40 can be easily stretched in this range A. In the ranges B, the continuous fibers 20 substantially have not been stretched and therefore it is not so easy in these ranges B as in the range A to stretch the covering member 40. Along the end portion 52 of the rear waist region 46, an elastic member 56 associated with the waist-opening is disposed between the inside sheet 40 a and the outside sheet 40 b and bonded to the inner surface of at least one of these sheets 40 a, 40 b.

[0032] In the case of this diaper 1 also, the pressure P exerted on the absorbent member 45 including the core member 44 is sufficiently absorbed by the range A of the covering member 40 being stretched to prevent the pressure P from affecting elastic members 57 associated with the respective leg-openings. With an advantageous consequence, it is not apprehended for this diaper 1 also that the pressure P might cause the members 57 to be disengaged from the wearer's legs and thereby cause sideways leak of excretion.

[0033] While this invention has been described hereinabove with respect to the open-type diaper 1 as a typical embodiment, this invention is applicable to a pants-type diaper. It is not essential to define the range A of the member covering the crotch and waist regions in which this member is more easily stretchable than the remaining zones in the transversely middle zone of the member but may be selectively defined in any desired zone.

[0034] In the disposable diaper according to this invention, the covering member adapted to cover the crotch and the waist regions is formed so that the covering member can be more easily stretched in its transversely middle zone than in its transversely opposite side edge portions. With this unique arrangement, the pressure exerted from the wearer's body upon the absorbent core member as the diaper is put on the wearer's body is substantially prevented from affecting the elastic members associated with the leg-openings. In this way, it is possible to eliminate an anxiety that the elastic members might be disengaged from the legs and, as a result, excretion might leak sideways. 

What is claimed is:
 1. A disposable diaper comprising an elastically stretchable covering member adapted to cover diaper wearer's crotch and waist regions and a liquid-absorbent core member sandwiched between a liquid-pervious sheet destined to come in contact with skin of said diaper wearer and said covering member, wherein: said covering member consists of an elastically stretchable first layer and an inelastically stretchable second layer formed with a plurality of continuous fibers and said continuous fibers being fixed to said first layer in at least a pair of bonding zones spaced from each other so that L/D, i.e., a ratio of a length L of said continuous fiber extending between said pair of the bonding zones to a distance D in straight line between said pair of bonding zones is larger in a desired range of said covering member than in the remaining zone.
 2. The diaper according to claim 1, wherein said desired range is defined in a transversely middle zone of said diaper.
 3. The diaper according to claim 1, wherein said first layer is formed with an elastically stretchable film or a nonwoven fabric made of crimped fiber.
 4. The diaper according to claim 1, wherein said continuous fibers of said second layer are made of polypropylene or propylene copolymer.
 5. The diaper according to claim 1, wherein said first layer is formed with a liquid-impervious sheet and lies inside said second layer.
 6. The diaper according to claim 1, wherein said first layer is formed with a liquid-impervious sheet and lies inside said second layer so that said first layer may be used as a liquid-impervious backsheet for said core member.
 7. A process for making a disposable diaper comprising an elastically stretchable covering member adapted to cover diaper wearer s crotch and waist regions and a liquid-absorbent core member sandwiched between a liquid-pervious sheet destined to come in contact with skin of said diaper wearer and said covering member, said process comprising the steps of: bonding an elastically stretchable first layer destined to form said covering member and a second layer formed with a plurality of inelastically stretchable continuous fibers together in a plurality of intermittently formed bonding zones and thereby to form a composite sheet, stretching only a portion of said composite sheet in one direction so that said first layer forming said portion may be elastically stretched together with said continuous fibers, and then leaving said composite sheet contract under a contractile force of said first layer to form said covering member. 